1. Field of the Invention
The present invention relates to surface-modified wholly aromatic polyamide filaments. Particularly, the present invention relates to surface-modified wholly aromatic polyamide filaments having a satisfactory bundling property and reeling property and thus useful for reinforcing synthetic resin articles.
2. Description of the Related Art
It is known that there is a strong demand for high quality synthetic filaments having a superior mechanical strength, modules of elasticity, and thermal resistance.
Also, it is known that various attempts have been made to provide filament-reinforced synthetic resin articles in which reinforcing filaments having a high modulus of elasticity are embedded in a synthetic resin matrix to enhance the mechanical quality of the substrate. Especially, it is well known that wholly aromatic polyamide filaments have a high mechanical strength, modulus of elasticity, and thermal resistance and thus are useful as a reinforcing material for various shaped synthetic resin articles.
Further, it is known that wholly aromatic polyamide filaments have a low elongation and a high dimensional stability and thus are useful as reinforcing material for rubber articles, for example, timing belts, which need a high dimensional stability.
Nevertheless, wholly aromatic polyamide filaments having a high modulus of elasticity are disadvantageous in that the filaments have a high rigidity and thus a poor bundling property. Also, wholly aromatic polyamide filaments have a poor surface activity and thus an unsatisfactory bonding (adhesive) property.
In particular cases, when a wholly aromatic polyamide filament cord is contained in a raw edge type belt in which a cut face of the filament cord appears in a cut face of the belt, the individual filaments located in the cut face of the belt are easily frayed and separated from each other.
To eliminate the above-mentioned disadvantages, Japanese Unexamined Patent Publication (Kokai) No. 59-94640 and Japanese Examined Patent Publication (Kokoku) No. 53-37473 disclose a treatment of a multi filament yarn or other filament articles with a treating agent comprising an epoxy or isocyanate compound before or after the yarn or article is formed from the filaments. The treated multifilament yarn or other filament article exhibits a high resistance to separation of individual filaments from each other, and a high bonding (adhesive) property. Nevertheless, the treated multifilament yarn or other filament article has disadvantages, for example, an excessively high rigidity or stiffness and a low resistance to flexural fatigue. Therefore, the amount of the treating agent that can be applied to the surface of each filament is limited to a very low level.
Also, in the treated multifilament yarn, the coating layer comprising the treating agent must be completely cured before the yarn is wound up into a package.
If the curing is not effected or completed, the treating agent in the coating layer is naturally cured with time and causes the wound multifilament yarns to adhere to each other, which makes them difficult to unwind from the package, and thus some individual filaments in the yarn are broken and form a number of fluffs.
This phenomenon can be avoided by completely curing the coating layer before the winding procedure, but a complete curing procedure takes a long time, and thus the whole process time becomes undesirably long or the process speed becomes undesirably low. Therefore, an industrial utilization of conventional epoxy or isocyanate compounds is very difficult due to the low efficiency thereof.
Japanese Examined Patent Publication (Kokoku) No. 63-20454 discloses a process for immersion-treating an aromatic polyamide filament yarn with a urethane-modified epoxy resin in the form of a solution in an organic solvent or of an aqueous emulsion, but was found that the resultant coating layer exhibited a poor mechanical strength and an unsatisfactory bonding property. Also the solution of the modified epoxy resin in the organic solvent causes inconvenience during handling. Furthermore, when the aqueous emulsion of the modified epoxy resin is prepared by using an emulsifying agent comprising a surfactant, the emulsifying agent causes the resultant aqueous emulsion to exhibit a lowered bonding property.
Accordingly, there is a strong demand for new wholly aromatic polyamide filaments free from the above-mentioned disadvantages.